1. Field of the Invention
The present invention relates to a structure to feed lubricating oil to the transmission shaft for the internal combustion engine of motorcycles and the like.
2. Description of Background Art
The transmission shaft connected to the internal combustion engine of motorcycles is equipped with some sort of lubricating oil feeding structure. A known example of them includes a main shaft functioning as the transmission shaft rotatably supported on the crankcase, a main lubricating oil passage that passes through the center of the main shaft, and multiple branch passages which radially branch off from the main passage, so that lubricating oil is supplied to the internal circumference of the gears mounted on the main shaft and the bearings to support the main shaft. See, for example, Japanese Patent Laid-Open No. 2006-77650.
The lubricating oil feeding structure disclosed in Japanese Patent Laid-Open No. 2006-77650 mentioned above has the following disadvantages. The bearings supporting the ends of the main shaft are widely open outward in both directions and this opening permits lubricating oil to flow in more than necessary for the bearings. This makes it necessary to supply the main lubricating oil passage in the main shaft with a large amount of lubricating oil for lubrication of various parts.